Excitatory amino acid receptors in glia: different subtypes for distinct functions?

It is now well established that expression of voltage- and ligand-gated ionic channels, as well as G protein-coupled receptors, is not a property unique to neurons, but is also shared by macroglial cells (astrocytes and oligodendrocytes). These glial cells can receive a variety of signals from neurons at different stages of their development. Activation of membrane receptors may affect glial cell activity, proliferation, maturation, and survival through a complex cascade of intracellular events leading to long-term changes in glial cell phenotype and functional organization. Here we review the experimental evidence for glutamate receptor expression in glial cells in culture and in situ, and the molecular and functional properties of these receptors. We also describe some experimental models that identify possible functions of glutamate receptors in glia. Now that the existence of glutamate receptors in glia has been unambiguously demonstrated, future research will have to 1) determine which receptor subtypes are expressed in macroglial cells in vivo; 2) analyze, in adequate experimental models, the short- and long-term changes produced by glutamate receptor activation in glia; and 3) establish whether these receptors play a role in neuron-glia communication in the brain.